The invention relates to a device for manufacturing thread-stitched book blocks which comprise folded printed sheets, the device having a conveying apparatus which transports the printed sheets astride a stitching saddle into a stitching position and being connected ahead of a feed apparatus for the printed sheets. Such device further has a stitching apparatus which is arranged at a lateral spacing from the stitching saddle and which can be driven in an oscillating manner transversely with respect to the conveying direction of the printed sheets which are transported by the conveying apparatus. The stitching apparatus can be supplied with printed sheets by the stitching saddle and the conveying apparatus is controlled so that the conveying speed and/or the stitching position of the printed sheets on the stitching saddle can be changed or can be adapted to the different properties of the printed sheets.
Devices of this type are known in thread-stitching machines for manufacturing thread-stitched book blocks; for example, in a thread-stitching machine INVENTA from Muller Martini Buchbindesysteme AG. Here, the printed sheets are gripped individually at the delivery end of the likewise saddle-shaped feed apparatus by the conveying apparatus which is assigned to the stitching saddle, and the printed sheets are displaced on the stitching saddle into a stitching position. As soon as the printed sheet has reached the stitching position, the frictional connection is released between the belts of the conveying apparatus which transport the printed sheet on the stitching saddle, and the stitching saddle is pivoted with the printed sheet into the stitching position of the stitching apparatus.
This largely inelastic drive connection to the transport means for the printed sheets does not permit precise positioning of the printed sheets on the stitching saddle which are defined for a book block, and the reliability and the accuracy suffers as a result when the printed sheets approach one another. A further impediment is that the properties of the different printed sheets which are defined for a book block, be they with regard to weight, thickness and/or quality of the material (for example paper), etc., tend towards an irregular behavior during the transfer from the feed apparatus onto the stitching saddle, for example by different slippage of the printed sheets in the conveying direction.
Because control can be lost over printed sheets, they recoil from stops or do not reach their stitching position on the stitching saddle.
In a device according to European Patent document EP 1 013 470 A1, the conveying belts of the conveying apparatus are fastened to the laterally movable stitching saddle, whereas the conveying apparatus is arranged at a fixed position in the above-mentioned thread-stitching machine INVENTA.
In both known devices, the printed sheets are gripped after the feed apparatus by the conveying apparatus which is assigned to the stitching saddle, and the printed sheets are preferably accelerated in the conveying direction, with the result that they are removed in time from the drivers of the feed apparatus, in order to be braked against a stop before they reach the stitching position, in order that a hard impact can be avoided.
Efforts have been made up to now to achieve this aim with a mechanical apparatus, but it can be achieved only imprecisely on account of the great variability of the formats and weights of the printed sheets and different friction conditions or different properties of the printed sheets which follow one another. Exact positioning has also not been achieved in the known manner. It is possible that the problem can be lessened by the costly exchange of control cams, but it cannot be completely prevented.